The companies decide the computer system must be up 24/7. Ok, fine. In the past things that needed to be running 24/7 were run by three shifts of workers. Companies could decide if the cost of 3 shifts was worth whatever value the system provided.
However, somehow with computers it's different. If there's a problem with a computer after hours the companies just call whoever was working during the day and expect them to fix it. Or they set up "on call" where you're explicitly expected to work all day and also all night.
They get away with this in the US because the meager workers rights laws in there (FMLA) explicitly exclude salaried computer workers from getting overtime[0]. So if you're a salaried computer worker and work all night because some system went down you're working for free and the companies love that because they don't have to do the calculation of whether having the system available is worth paying someone to watch it.
So take the stress from receiving an after hours email and multiply it by 100x because now you're not only expected to reply to the email but to drop everything and fix the computer.
This is also why companies that depend on computers need so many foreign workers living locally on temporary visas. They can be abused this way but can't fight back without risking losing their jobs and being deported.
Either IT workers need to unionize or the US needs to rewrite labor law to prevent this kind of abuse.
0: https://www.dol.gov/agencies/whd/fact-sheets/17e-overtime-co...